1. Field of the Invention
The present invention relates to a motor driving device.
2. Description of the Prior Art
Motor driving devices are known that are provided with a drive circuit for driving a motor and a protection diode for preventing the drive circuit from being destroyed when a power source is connected thereto with reverse polarities. FIG. 2 shows an example of a circuit configuration of an output stage of a pre-drive circuit 1 for a two-phase half-wave fan motor. A MOS-type field-effect transistor (or bipolar transistor) 100 an a resistor 200 are connected in series between a supplied-power terminal T1 and a ground terminal T2. A node between the transistor 100 and the resistor 200 is connected to an output terminal T3.
In actual use, to the output terminal T3, the base of an NPN-type power transistor 3 is connected through resistor 6. The transistor 3 has its emitter grounded, and has its collector connected to one end of a coil 4 of a fan motor. The other end of the coil 4 is connected to a cathode of a diode 5. An anode of the diode 5 is connected to a supplied voltage Vcc.
With a motor driving device provided with the pre-drive circuit 1 as described above, there is a risk of a power source being connected thereto with reverse polarities, for example, as a result of improper insertion of a connector. Therefore, to prevent destruction, resulting from reverse connection of a power source, of the circuit elements, such as the MOS transistor 100, constituting the pre-drive circuit 1, it has been customary to connect to the supplied-power terminal T1 of the pre-drive circuit 1 the cathode of a protection diode 2 of which the anode is connected to a terminal (not shown) to which the supplied power is supplied.
Here, the current that flows into the base of the transistor 3 to drive the motor is supplied directly from the power source, and therefore the protection diode 2 needs to have a high current capacity. In general, however, it is difficult to obtain a satisfactorily high current capacity with a diode formed within an IC (integrated circuit). For this reason, usually, in FIG. 2, whereas the pre-drive circuit 1 is formed as a one-chip IC, the protection diode 2 is connected externally to the IC. As a result, conventional motor driving devices provided with a pre-drive circuit and a protection diode has the disadvantage of requiring an unduly large mounting area and also requiring an extra assembly step.
The same problem is addressed by Japanese Patent Application Laid-Open No. H7-130927, which proposes, as a solution, mounting a MOS transistor and a diode on a single island. However, this is possible only with a single MOS transistor; that is, with a common IC, which is not formed on a single substrate together with a diode, it is impossible to mount the IC and the diode on a single island.
An object of the present invention is to provide a motor driving device that, despite being provided with a drive circuit for driving a motor and a protection diode, requires a reduced mounting area and a reduced number of assembly steps.
To achieve the above object, according to the present invention, a motor driving device is provided with: an IC chip incorporating a circuit for driving a motor; a diode chip provided in a power-supply path through which electric power is supplied to the IC chip; a leadframe having a first island on which the IC chip is mounted and a second island on which the diode chip is mounted; a wire connecting together a supplied-power island provided on the IC chip and the second island; and a package incorporating the leadframe, the IC chip, and the diode chip.
This structure eliminates the need to connect a protection diode externally. Moreover, this structure makes it possible to obtain not only a higher current capacity but also a higher peak inverse voltage in the protection diode than when it is formed within an IC.